The Camp Nesbit Ropes Course

  • U.S. Forest Service officials were concerned about the safety of a ropes course used by elementary, middle, and high school students at Camp Nesbit in Michigan’s Ottowa National Forest.
  • The Forest Products Laboratory (FPL) was asked to assemble a team of experts in decay detection, which included R. Bruce Allison, to conduct a thorough examination of the 16 red pines that serve as the frame for the ropes course.
  • Initially, Allison and the team conducted single-path acoustic testing on the trees, measuring the speed of sound waves traveling through the tree at various heights. Slower speeds can indicate decay, cracks, or other imperfections in the tree.
  • Acoustic tomography was then performed on the lower areas of each tree to generate an image indicating the condition of the trees’ interior.
  • The team carefully examined the tomography results and conducted an experiment comparing two different tomography tools to see which gave a more accurate prediction of the internal condition of the trees.
  • Allison and FPL’s Xiping Wang then conducted resistograph tests on the trees where the tomographs indicated a problem. A micro-drilling tool was sent through the tree, measuring the torque resistance with the length of the measurement. The data collected was then used to create a graph showing areas of defect, crack, or cavity.
  • As it turned out, the tools for detecting internal decay had accurately shown the significant amount of decay, further justifying the removal of the tree from the ropes course.